In the production of minerals, specifically oil and gas, it is common to "engineer" the producing reservoir to improve the economic performance thereof. To do this, certain lithological properties of the reservoir must be determined, the two most important of these properties being the permeability and the porosity of the reservoir rock. Permeability is a measure of the ability of a material to transmit fluids through pore spaces of the mineral and is inversely proportional to the flow resistance offered by the material. Porosity of a material is defined as the ratio of the aggregate volume of its void or pore spaces to its gross bulk volume. In the case of an oil reservoir, porosity is a measure of the volume within the reservoir rock which is available for storing oil and gas.
Normally, porosity and permeability of a reservoir rock are determined from core samples by applying well-defined measurement procedures, such as those described on pages 660-669, Petroleum Production Engineering-Development, by L. C. Uren, Fourth Edition, McGraw-Hill Book Company, Inc., 1956.
Prior to carrying out such porosity and permeability measurements, as well as other desired measurements, it is the usual practice to clean the core sample of brine, salt deposits, residual hydrocarbons, and solid contaminant particles, such as rock microfragments and drilling mud solids. One of the standard cleaning methods is to flush the core sample with liquid toluene and carbon dioxide gas. The problem with this method is that carbon dioxide attacks the core sample itself. Other non-flushing methods have also been suggested and tried, such as ultrasonic cleaning. The present invention is directed to a new method for cleaning a core sample in which a dynamic evolution of a dissolved gas previously injected into the core sample in a liquid solution is utilized to carry solid contaminant particles from within the core sample to the outer surface of the core sample.